Currently, in the clinical setting of open heart surgery, several anticoagulation assays are used to monitor heparin therapy. While these methods for monitoring heparin are effective, they require eight to ten minutes or more to run, several steps of blood handling, as well as instruments to make an end point reading. Also, these current assays only indicate a biological response and provide, at best, an indirect quantitative measure of heparin. With over 350,000 open heart procedures per year in the U.S., where high dose heparin is administered and must subsequently be reversed, the need for rapid, low cost, quantitative assay for blood heparin is well recognized. It is the overall goal of the proposed work to develop a diagnostic assay that will accurately measure the amount of heparin in an accurate, quick (less than 1-2 min.) and cost effective fashion. A novel feature of the proposed heparin assay is that even relatively high heparin concentrations would not necessarily require greater time for testing. By the end of Phase 1, a prototype assay will be tested against standard laboratory assays utilizing fresh collected blood bank blood to characterize correlation coefficients amongst heparin assays in the Phase 11 studies. Preliminary in vitro tests show that clot formation times can be reduced by 35% to 50%; greater reduction can be expected.